In petroleum and natural gas exploitation fields, in order to prevent sand in the oil-gas well from being brought to shaft or ground apparatuses together with oil-gas-water while sanding, in-well screen which could effectively filtrates oil-gas-water needed to be used. One hole in a segment of an in-well screen ranged from several decades to several hundred meters would destroy the whole sand protection in-well project. If the sand protection fails, normal production of the oil-gas well will be influenced or the oil-gas well will be discarded. Thus filter materials of screen thus need to possess the following comprehensive property: exactly controllable pore size, strong whole strength, flexibility, excellent corrosive resistance and high reliability.
At present, most of filter materials used to make premium screen are very expensive multi-layer sintered metal net. This multi-layer sintered metal net is porous filter material produced by vacuum welding technology. It is a composite made of multilayer metal net, metal fiber or metal powder and has better solderability. It can be welded by arc welding or plasma arc welding without leaks and guarantee the welding strength. However, the filter material has high factory cost, low productivity and its size is limited by vacuum welding apparatus.
Using metal net to take place of above-said sintered filter material will have high economic benefit. However, conventional welding technology has either low welding strength or leak phenomena (shrinkage hole phenomena) appears on welding parts of melt net. When using single-layer metal net as filter material of screen, welding pores will appear on arc welding parts. Therefore, single-layer metal net is fixed on base pipe of screen by way of mechanical fixing means (e.g. hem and compacting means etc). However, the strength and reliability produced by these methods are relative low.
Although the screen may be made of non-sintered multi-layer composite net, during welding, shrinkage hole phenomena of multi-layer compound net is more serious than single-layer metal net. At the same time, due to high thickness of screen and several-meter-long filter segment, series of difficulties are brought to welding procedure. Thus how to obtain high quality and low cost screen welded by way of welding method from metal net is one big problem in the field.